Ordered the lookup of machine IDs to guard against randomly ordered map ...

In Go v1.3, map ordering was intentionally randomized to discourage relying on maps which were coincidentally ordered how expected. This corrects a non-deterministic bug in one of the tests which was caused by this change to Go.
Since this is a map, I don't think we can access the index that a machine ID resides in. In regards to your second comment, I feel that the intent of the variable is to contain a list of sorted machine ID's. Of course it can't be initialized as such, but that is the working, and only goal. As such, I'd prefer to keep the name.